Pirich's Full Review: Celestron NexStar 6 SE (354 x 55.88mm) Telescope
Compared to their diameter, the Schmidt Cassegrain Telescope (SCT) is the most compact design yet derived. It has been over a decade since the last new SCT design came from Celestron, the company who pioneered their commercial manufacture forty years ago. This new scope comes in a useful size with a computer driven mount derived from the one used with the NexStar 5i. This variant is still very compact, and it offers a lot of telescope for the money. More general information on telescopes can be found in my article on Picking a Telescope.
Background
The SCT is a multi-purpose telescope with a secondary mirror in the center of a glass corrector plate which puts the image conveniently at the back of the telescope. This design is extremely compact; no other design will pack as much aperture or focal length into less space. Tom Johnson started Celestron Pacific in the 1960s, and the product he loosed on the world was a series of SCTs sized so amateur astronomers could own unusually flexible telescopes in an era when you could either get a very long focal length refractor or a moderate focal length Newtonian, and that was it.
In 1970, Celestron introduced an 8" diameter SCT they had developed after a decade of making various models in small numbers, and the combination of mount and aperture took off, and it was 10 years before anything challenged it, and when it did, it was in the form of refractors so expensive they were destined to be high-end boutique specialties for the next twenty years.
But now things are changing again. We are in the closest thing there has ever been to a golden age of telescopes. Superb scopes of every sort are now available at lower prices than ever. After twenty-five years as high end luxuries, Apochromatic (APO or ED) refractors have come down in price enough for the three major types; Refractors, Newtonians, and SCTs to be a buying decision based on weighing technical merit directly against cost.
This is a quick listing of design characteristics for different types to help consider the NexStar 6SE against:
Refractor:
-Best performance compared to diameter.
-Cost of a this 6" GOTO SCT equates to an 80mm ED refractor on a GOTO mount.
-Limited focus range due to draw tube.
-Large movement of eyepiece relative to ground.
-Long optical tube (focal length + 20%)
-Works well for photography
-High contrast images if false color well corrected.
Newtonian:
-Lowest cost compared to diameter. 6" GOTO SCT translates to a 12" newtonian on a dobsonian mount, or a 10" newtonian on a GOTO equatorial mount.
-Limited focal range due to focuser on side of tube.
-Unusual image orientation.
-Physically bulky
-Continuing realignment (recollimation) maintenance required.
SCT:
-Very compact mount and scope is easily portable.
-Largest possible focus range.
-Less eyepiece travel as scope moves.
-Scope can use the Celestron Focal Reducer to move between f/10 and f/6.3.
So, what is special about the Schmidt Cassegrain is its portability, ability to bring just about anything to focus, ease to convert to radically different focal ratios, and moderate cost. In other words, lowering the cost of the high quality refractor doesn't make it an ideal general purpose telescope, since a 6" refractor is still going to be 5 feet long.
The NexStar 6SE is a new size for Schmidt Cassegrains. The 8" variant from Celestron dates from 1970, and the 5" first appeared in 1971. No in-between size has come about until 2006. The 8" and the 5" have a very large difference in diameter and area, and are radically different in size. The 8" scope is the size of a 2 gallon paint pail, while the 5" is the size of a coffee can. The difference in light gathering area is over 2.5:1, so the 8" is physically a much bigger telescope than the C5.
I have wondered if something in between was feasible. If the 5" NexStar is compared to the 6" NesStar, it is a price difference of $200 to get 44% more light gathering area. Between the 6" and the 8", the difference is $400 to get 78% more area. Strangely, the 6" comes on both the single arm fork mount this review is about, or a computer guided German equatorial at the same price. The 8" scope is $100 more on the same German Equatorial than it is on this fork mount.
Description and Usage
The NexStar 6SE can't hide in the corner; it's metallic orange. Celestron made orange telescopes back in the 1970s when orange was kind of cool. Now, orange is cool again, and the scopes are glittering orange, like an automotive paint. The rest of the assembly is black, and the tripod is in polished stainless steel. All in all, it looks sharp enough for the living room.
The 6" barrel is similarly proportioned to the 5" scope, but it is obviously larger in all dimensions. So, while it is larger than a NexStar 5i, it is still very compact compared to the 8" scope. The fork mount is a development from the one used for the NexStar 5, 5i, 8, 8i, and is also on the NexStar 8SE. In a welcome nod to practicality, this scope is mounted to its fork arm with a Vixen dovetail. This means you can loosen this scope and scoot it forward to balance it with a heavy Digital SLR mounted on the back (I have been using a Maxxum 7D this way). The dovetail also means you can release the dovetail and completely remove the optical tube from the fork for convenient transport, or mount another scope, including refractors such as the Onyx 80ED Refractor or the AT-66ED So, you could take a couple scopes along to the countryside and share one mount. I have been doing this with the older C5+ mount, and it works very well for small refractors.
The NexStar 6SE we used was driven off of a large battery, and from my previous experience with the other large NexStars, I knew a fresh set of AA batteries was only good for one night of observing. The three star alignment this mount uses was done simply by turning on the mount (there is a now a red ON light) and then putting in the location (it has a list of cities, so this is easy), then driving to the three brightest stars in the sky.
Interestingly, the performance was radically different than the related NexStar 102, which was unable to make an alignment unless it has full voltage getting to it. This scope took the alignment on the first try, and the pointing accuracy after aligning to three stars in different parts of the sky was quite impressive. This low-care alignment was as good as the more careful alignments I have done with the NexStar 8 GPS using a reticle eyepiece.
The NexStar 6SE mount slews quickly and with authority to viewing targets. From previous experience with the NexStar 5, these mounts get strange on you if they start running low on power. They won't put up a low battery indicator, but instead some of their functions won't work so well- usually it has the form of getting a bit lost. I recommend getting the AC adapter to save on battery costs.
The tripod has asmall tray, which presents one of the larger problems- where does the front lens cap go? I suggest getting round velcro stick-on pads and putting one on the center of the outside of the lens cap, and one on one of the tripod legs to hang the cap sideways so dew doesn't form on it and dust does not get in it.
Optically, this telescope is an interesting mix between the C5 and the C8. Its absolute resolution capability is only 20% different from the C5, so objects are very similar in appearance and resolution. The 6SE shows a beautiful sharp image on Saturn, and the Moon has sharp detail. On the Orion Nebula, this scope shows four pinpoint stars in the trapezium (a good 8" scope shows 6), so the resolving power is more like the C5 than the C8. The other difference is the Plieades don't quite fit into one field at low power, though they are razor sharp blue-white pinpoints across the field. I didn't have a chance to try the focal reducer, but with the 945mm focal length in that configuration, the Plieades should just barely fit.
In the mechanics of the mirror system, this scope is a bit more like the C8. The mirror does shift when you go from moving in to out on focus. The C5 is completely shift-free, which makes using it a pleasure. The mirror shift in the 6SE is about as much as I see in the NexStar 8 GPS, which means you go from being able to roll back and forth across focus to a method where you purposely drive across focus a few times to figure out where it is, then drive back to it from one direction and STOP.
I came away feeling this scope is very nice, but I have no urge to replace the C5 with one. I can see how its resolution on planets would make this a very satisfying scope if it is your only telescope. That, combined with the ability to swap in other optical tubes makes a really neat package, especially since you can save money by getting a small wide-field refractor as a separate optical tube. You will need to get a dovetail bar from Orion (www.telescope.com- search on Dovetail), more detail is in my review of the Orion Dovetail.
Single arm mounts sometimes get comments like "Is it stable?" When nudged, the mount damps out the shakes within 2 seconds, even with large taps. I am not sure why people have a thing for single arms- after all, all German equatorials have one arm, and heck, even the wing of a 747 is connected as one arm. The NexStar mount is a single piece aluminum casting, and it is very stout as a result. Unfortunately, this mount is not going to be capable of long exposure photography for an unexpected reason; the tracking isn't uniform. The story behind this is in my article on the equatorial wedge designed for this mount.
Conclusion
The NexStar 6SE easily fills a role for a general purpose telescope. The NexStar control system on it is mature at this point and organic to the telescope. Between this and the smaller NexStar 5, I still feel the 5" does 90% of everything, but this one will have a small edge in resolution. The NexStar 6SE goes outside all in one lift, so it meets the requirements for a quick observing session. If you want to do astrophotography, this mount will not allow long exposures due to non-uniform tracking. If that is your goal at the outset, the version sold on a German equatorial mount does the necessary tracking and it is cheaper, though heavier and larger. All in all, the NexStar 6SE is a very satisfactory telescope system. Currently Celestron is offering a $150 rebate which makes the full-up cost of one of these systems about $800, or to put it another way, within $100 of the toylike Meade ETX-90, which this telescope absolutely eclipses in performance. The NexStar 6SE actually costs $75 less than the currently discounted Meade ETX-125 which it also decisively outperforms. The net result is an extremely capable telescope.
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